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.\" $NetBSD: affinity.3,v 1.10 2025/02/25 10:15:41 riastradh Exp $
.\"
.\" Copyright (c) 2008 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Mindaugas Rasiukevicius <rmind at NetBSD org>.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
.\" POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd February 21, 2025
.Dt AFFINITY 3
.Os
.Sh NAME
.Nm pthread_setaffinity_np ,
.Nm pthread_getaffinity_np
.Nd affinity of threads
.Sh LIBRARY
.Lb libpthread
.Sh SYNOPSIS
.In pthread.h
.In sched.h
.Ft int
.Fn pthread_setaffinity_np "pthread_t thread" "size_t size" "cpuset_t *set"
.Ft int
.Fn pthread_getaffinity_np "pthread_t thread" "size_t size" "cpuset_t *set"
.Sh DESCRIPTION
Thread affinity allows to run the thread on specified CPU or CPUs only.
.Pp
The
.Fn pthread_setaffinity_np
function sets the affinity mask
.Fa set
for
.Fa thread .
At least one valid CPU must be set in the mask.
.Pp
The
.Fn pthread_getaffinity_np
function gets the affinity mask of
.Fa thread
into
.Fa set .
Note that
.Fa set
must be created and initialized using the
.Xr cpuset 3
functions.
.Sh IMPLEMENTATION NOTES
Setting CPU
.Nm
requires super-user privileges.
Ordinary users can be allowed to control CPU affinity
of their threads via the
.Pa security.models.extensions.user_set_cpu_affinity
.Xr sysctl 7 .
See
.Xr secmodel_extensions 9 .
.Pp
Portable applications should not use the
.Fn pthread_setaffinity_np
and
.Fn pthread_getaffinity_np
functions.
.Sh RETURN VALUES
The
.Fn pthread_setaffinity_np
and
.Fn pthread_getaffinity_np
functions return 0 on success.
Otherwise, an error number is returned to indicate the error.
.Sh EXAMPLES
An example of code fragment, which sets the affinity for the current
thread to the CPU whose ID is 0:
.Bd -literal
cpuset_t *cset;
pthread_t pth;
cpuid_t ci;
int error;
cset = cpuset_create();
if (cset == NULL) {
err(EXIT_FAILURE, "cpuset_create");
}
ci = 0;
cpuset_set(ci, cset);
pth = pthread_self();
error = pthread_setaffinity_np(pth, cpuset_size(cset), cset);
if (error) {
errc(EXIT_FAILURE, error, "pthread_setaffinity_np failed");
}
cpuset_destroy(cset);
.Ed
.Sh COMPATIBILITY
Both functions are non-standard extensions.
.Sh ERRORS
Both functions may fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The specified
.Fa set
was invalid.
.It Bq Er EPERM
The calling process lacks the appropriate privileges to perform
the operation.
.It Bq Er ESRCH
No thread could be found corresponding to the one specified by
.Fa thread .
.El
.Sh NOTES
There is an alternative processor sets interface, see
.Xr pset 3 .
However, thread affinity and processor sets are mutually exclusive,
hence mixing of these interfaces is prohibited.
.Sh SEE ALSO
.Xr cpuset 3 ,
.Xr pset 3 ,
.Xr pthread_getschedparam 3 ,
.Xr pthread_setschedparam 3 ,
.Xr sched 3 ,
.Xr schedctl 8
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